1. Field of the Invention
The present invention is directed to an output and input coupler for multi-mode glass fibers and the method of making the coupler.
2. Prior Art
In a glass fiber transmission system, it is often necessary to output couple a part of the optical power from a glass fiber at a specific point or to additionally input couple optical power into the glass fiber system. The output coupling of a part of the optical power of the system enables supplying a subscriber with a signal or to measure the signal level in the line. The input coupling enables a subscriber to feed a signal into the transmission lines.
Output and input couplers for groups of glass fibers are already known. Examples of these couplers are described in the following two publications: F. L. Thiel, "Topical Meeting On Optical Fiber Transmission", Jan. 7-9, 1975, Williamsburg, Virginia, U.S.A., Paper WE 1-1 and A. F. Milton, A. B. Lee, "Topical Meeting Of Optical Fiber Transmission", Jan. 7-9, 1975, Williamsburg, Virginia, U.S.A., Paper WE 2-1.
Another known type of glass fiber branch arrangement is a branching fiber core which is arranged within a common fiber cladding. This known branching arrangement could also be used as an output and input coupler. This known branch arrangement was produced by providing a preform having a branched core, and then drawing the preform to form the appropriate branched glass fibers. However, the production process to produce this type of branched glass fiber is relatively expensive.